Changes fall into these categories:
1. Avoid pathological string building. Loops over x = x .. "foo" can
become very slow. Instead, use strbuf.lua, table.concat, or just one
continuous concatenation; a = x .. y .. z is one operation, better than
a = x .. y; a = a .. z
2. Use hex-escaped strings instead of string.char. I find this more
readable in many cases, and it avoids a table lookup and function call.
3. Don't duplicate code. A few libraries and scripts had re-implemented
stdnse.generate_random_string or openssl.rand_bytes.
stdnse.print_debug accepts a format string and arguments, making
string.format redundant in calls of this form:
stdnse.print_debug(1, string.format("%s: error", SCRIPT_NAME))
stdnse.print_debug(("length %d"):format(#tab))
These can be rewritten as:
stdnse.print_debug(1, "%s: error", SCRIPT_NAME)
stdnse.print_debug("length %d", #tab)
